The river rises in the heart of the Warrumbungle mountains and initially flows east through the town of Coonabarabran. It then follows a looping course to the south, west, and finally northwest, joined by 26 minor tributaries, towards its confluence with the Macquarie River; dropping 509 metres (1,670 ft) over its course of 541 kilometres (336 mi).[2] The Castlereagh River has a highly variable flow, and often, low to no flow.[3]